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 p.11 #9 · ['NEW Fix' UPDATE!] - MkIII AF still broken | |
Jeff wrote:
That's a good question Alistair, and I made very sure of this one last night before I posted it (I should have included the loupe, but ran out of time, what with all the errant rhetoric being slung about).
The focus was on the tree in the center, and both sides of the rock were roughly equidistant to my position. Even if what you suggest were true, you should be able to move 'backward' on the right hand pillar of rock until you find the focal plane, but you cannot. There is absolutely nothing in focus in the right half of the frame, but there should be. At that distance to subject, the left side of the frame exhibits the depth of field one would expect with this lens and f/stop combination; the right is inexplicable for normally-operating equipment, in my opinion.
Now, turn this picture vertically, and let's analyze this in relation to the oft-repeated (by myself and many others) 'running sequence using AI Servo'. (Lots of 'ifs' here, so forgive the following) Now imagine the bottom half of the image being the sharp portion, and the top part being the out-of-focus portion. You would be able to precisely find a plane of focus near the runner's feet, where it is very easy to determine due to the grass. Some of the runner's legs/torso may be sharp, as you near the halfway point of the frame. As you move toward the shoulders and face, it becomes harder (and in some cases impossible) to find where the plane of focus goes through the 'meat' of the image. Nothing near the face is obviously in focus, and what is 'most in focus' is still quite soft.
I cannot tell you how many times I've seen this exact effect, and it can be seen in many of RG's sequences. Many people have noted not being able to find something in a given image that is critically sharp, with no obvious cause. Many of these 'runner' sequences are heavily scrutinized for front- and backfocusing, and using the face (the primary subject) it is often difficult or impossible to determine, because nothing in that half of the frame is sharp.
It is thus entirely possible that much of what has been attributed to misfocusing (a la the submirror) was actually this 'plane of focus' effect in concert with the (pre-Blue Dot) jumpy AF, making it very, very difficult to isolate as a discrete problem. Whether or not the 'ghosting' issue is the same source is anyone's guess. Time will tell now that repaired cameras are starting to become more numerous, and I admit that these effects are sometimes very hard to see unless viewed at 1:1 or printed very large.
Respectfully,
Jeff
PS: Writing the above has reminded me of several instances in which I manually focused the MkIII, only to end up with a soft image. Going to have to scratch my head on this one, and see if I can find examples......Show more →
Is it at all possible that this is, rather than an IS issue, a question of the AF motor being driven during the actual exposure? I realize that this would not so readily explain the apparent variation in focus across the frame (and can't be the explanation for the fuzzy shots you did with MF), but maybe it could explain some of the erratic results. Malfunctioning IS seems much more probable for explaining what you've described and demonstrated, but if Galbraith's tests were done with IS off...
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At least my 6-year old got a bit faster this fall! 
